1. Field of the Invention
This invention relates to a process for removing water from carbonaceous materials and is particularly applicable to the dewatering of water-slurried coal although it may also be used as a means of mine-mouth beneficiation and for the separation of water from other solid organic materials containing same.
2. Analysis of the Prior Art
Pipelining coal as a slurry is being done successfully but experts in the field feel there is no practical method of slurry utilization. The coal slurry in question contains 40-60 percent of water and feeding this material directly to a boiler results in a large heat loss and makes the down stream separation of particulates difficult due to increased exhaust gas (steam, CO.sub.2, etc.) volumes. One coal-slurry dewatering plant dries the coal by the successive steps of vacuum filtration followed by thermal drying with flue gas-air mixture in a lift-pipe. The coal is effectively dried but energy costs are high and the dry coal dusts extensively despite the use of cyclones. Thus the hazards of atmospheric pollution are substantial. In another method the coal is dewatered to 15-10 percent water content by the use of centrifuges. The use of centrifuges in this service are accompanied by high investment and service costs plus the fact that the coal is only somewhat more than 50 percent dewatered. Obviously, this lower water content is an advantage over feeding the slurry directly to the boilers but the advantages of high energy costs and high concentrations of steam in the exhaust gases remain.
The prior art is also aware of the technology described in coassigned U.S. Pat. Nos. 2,999,741 and 3,846,087. These patents are concerned with the removal of soot from the quench water used in the production of synthesis gas. In accordance with the methods of those patents, the quench water containing only 1 to 2 percent of carbon is extracted with a liquid hydrocarbon mixture at a pressure of about 250 psig and 2500.degree. F. In the process of U.S. Pat. No. 3,552,031 moist solid organic material is subjected to a temperature of 240.degree. to 260.degree. C. and a pressure between the saturation pressure and 500 psig to separate liquid water from such material while the material is under such pressure.